Flowering is a term used to describe one type of instability of a pallet load (unit load). As illustrated in FIG. 1, flowering is a condition where columns of boxes 20 spread apart or lean away from each other as a pallet 10 is lifted or moved. This condition is a common occurrence in industry.
Flowering is most readily seen when a load, column stacked boxes for example, that had been loaded on a pallet deck 12 in a stable manner with the columns immediately adjacent to each other is lifted by a fork lift or pallet hand jack positioned within the openings 16 between the legs 14 of the pallet 10. Because the areas where the forks make contact with the pallet 10 are inset from the edges of the pallet deck 12, a portion of the load acts upon the portions of the pallet deck 12 that are cantilevered out beyond the support. The effect is typically to bend the outside of the edges downward and, often, to bow or raise the center of the pallet. The originally planar top surface 13 becomes convex.
As the top surface 13 of the pallet deck 12 becomes convex, the bottom box of each column stays in contact with the surface. As a result, the remaining boxes in the column flare or flower outward. As the columns continue to flower outward, they move farther away from the surrounding columns and the load becomes less and less stable, possibly falling over.
The same effect may be seen as a pallet moves on a conveyor. Depending on the pitch of the rollers, the distance between adjacent rollers, or the severity of transition points between conveyors, loaded pallets may bow in a manner similar to being lifted by a fork truck.
Flowering is typically counteracted by wrapping the load. In some instances, just the top portion of the load may be wrapped using strapping or stretch wrap. More often, the entire load is secured with strapping or wrapped with stretch wrap.
Strapping or wrapping of the unit loads adds cost. Slower line throughputs, for strapping/wrapping or unstrapping/unwrapping, additional labor, again for strapping/wrapping and unstrapping/unwrapping, additional material, additional equipment, additional floor space, the strapping/wrapping materials, and disposal of the strapping/wrapping materials may all be components of these increased costs. While strapping/wrapping can counteract some of the instability, it cannot stop instability of the load moving on a conveyor or moving through production processes prior to the strapping/wrapping point. Further, if the unit loads are work-in-process materials or are to be broken down for customer specific orders, the pallets may have to be strapped/wrapped and unstrapped/unwrapped multiple times before eventually being shipped.
As another potential problem, a unit load traveling through a packing line or supply chain it is subject to many different forces acting upon it, including vibration. A unit load traveling down a conveyor line or being moved by fork lift across an imperfect floor are common examples of this issue. As the load is vibrated, the columns of boxes 20 may separate or move toward the edge of the pallet deck 12. Both situations reduce the overall stability of the unit load.
Additionally, a unit load will experience centrifugal forces and lateral forces as it moves through production lines and supply chains. These forces will act to destabilize the load. These forces, for example, may result from curves and stopping points in a conveyor line; turns or stops made by a fork lift, or turns and stops made by a truck carrying the unit load.
A simple definition of centrifugal force is “a force that causes an object moving in a circular path to move out and away from the center of its path.” Lateral force is defined as a force whose main components are acting in a generally horizontal direction. The effects of the centrifugal and lateral forces are to move the center of gravity of a column of boxes on a pallet toward the outside of the pallet. For the column of boxes to remain stable, the center of gravity must remain within the base of support—the bottom of the lowest box. If an object is tilted it will fall over if a vertical line from its center of gravity falls outside its base.